I would recommend anyone using NixOS in production to use the release versions. That's what I do on my servers.. Like for other distros, the point of releases

I would recommend anyone using NixOS in production to use the release versions. That's what I do on my servers.. Like for other distros, the point of releases is that they don't upgrade random software under your feet, resulting in unplanned behaviour changes and unplanned required maintenance. Like for other distros, release channels get important upgrades and minor bugfix releases of upstream software. NixOS releases are every 6 months, so that's frequent enough to have pretty up-to-date software most of the time. NixOS also makes it very easy to cherry-pick fixes from master and make custom changes (it's just a /git cherry-pick/ away), allowing to selectively upgrade things that you need for your use case.